phase A: ai:alice writes handoff to ai:bob (uuid=h-fb9b7a117e3547f6837679ca9c6601e9)
settle 8s for quorum fanout
phase B: ai:bob reads handoff on node-2
  ai:bob sees 1 handoff memories from ai:alice
phase C: ai:bob writes acknowledgement (uuid=a-7469ea28d1db4e4d9bf947dff2e2bb60)
settle 8s for reverse-direction fanout
phase D: ai:alice reads ack on node-1
  ai:alice sees 1 ack memories from ai:bob